Solid state structures and solution behavior of titanium(IV) octahydrobinaphtholate complexes. Examination of nonlinear behavior in the asymmetric addition of ethyl groups to benzaldehyde

Article abstract of DOI:10.1021/om034107h

In several asymmetric reactions, H₈-BINOL-based catalysts (H₈-BINOL = 5,5′,6,6′,7,7′,8,8′- octahydro-1,1′-bi-2-naphthol) exhibit higher levels of enantioselectivity than analogous catalysts based on BINOL. A comparison of structures of titanium complexes prepared from H₈-BINOL and BINOL was, therefore, undertaken. Reaction of (rac)-H₈-BINOL with 1 equiv of titanium tetraisopropoxide resulted in formation of the dimer (meso)-[(H₈-BINOLate)Ti(O-i-Pr)₂]₂ [(meso)-6], which was characterized crystallographically. In a similar fashion, use of (rac)-BINOL led to formation of the dimer (meso)-[(BINOLate)Ti(O-i-Pr)₂]₂ [(meso)-7]. The torsional angles between the aryl rings of the H₈-BINOLate and BINOLate ligands in these complexes were 63.2(5)° and 55.7(4)°, respectively. The larger torsional angle of the H₈-BINOLate ligand results in an increase in the bite angle of the ligand by just over 2°. Upon dissolving dimers (meso)-6 and (meso)-7, equilibria between the homo- and heterochiral dimers were observed. Reaction of H₈-BINOL with an excess of titanium tetraisopropoxide provided crystals of the dinuclear complex [(H₈-BINOLate)Ti(O-i-Pr)₂]·Ti(O-i-Pr)₄ (8). Likewise, reaction of 2 equiv of Ti(OCy)₄ (Cy = cyclohexyl) with H₈-BINOL furnished [(H₈-BINOLate)Ti(OCy)₂]·Ti(OCy)₄ (9). These compounds were characterized by X-ray crystallography and compared to the known [(BINOLate)Ti(O-i-Pr)₂]·Ti(O-i-Pr)₄, a proposed intermediate in the asymmetric addition of alkyl groups to aldehydes. The solution behavior of 8 and 9 was studied by NMR spectroscopy, revealing that both complexes in solution are in equilibrium with dimers and free titanium tetraisopropoxide. Nonlinear studies with catalytic H₈-BINOL and an excess of titanium tetraisopropoxide in the asymmetric addition of ethyl groups to benzaldehyde showed no nonlinearity, suggesting that the equilibrium strongly favors formation of dinuclear 8 under the conditions of the asymmetric addition.

Full text of DOI:10.1021/om034107h

Organometallics 2004, 23, 127-134
127
Solid Sta te Str u ctu r es a n d Solu tion Beh a vior of
Tita n iu m (IV) Octa h yd r obin a p h th ola te Com p lexes.
Exa m in a tion of Non lin ea r Beh a vior in th e Asym m etr ic
Ad d ition of Eth yl Gr ou p s to Ben za ld eh yd e
Karen M. Waltz, Patrick J . Carroll, and Patrick J . Walsh*
P. Roy and Diane T. Vagelos Laboratories, Department of Chemistry, University of
Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323
Received August 12, 2003
In several asymmetric reactions, H8-BINOL-based catalysts (H8-BINOL ) 5,5′,6,6′,7,7′,8,8′-
octahydro-1,1′-bi-2-naphthol) exhibit higher levels of enantioselectivity than analogous
catalysts based on BINOL. A comparison of structures of titanium complexes prepared from
H8-BINOL and BINOL was, therefore, undertaken. Reaction of (rac)-H8-BINOL with 1 equiv
of titanium tetraisopropoxide resulted in formation of the dimer (meso)-[(H8-BINOLate)Ti-
(O-i-Pr)2]2 [(meso)-6], which was characterized crystallographically. In a similar fashion, use
of (rac)-BINOL led to formation of the dimer (meso)-[(BINOLate)Ti(O-i-Pr)2]2 [(meso)-7]. The
torsional angles between the aryl rings of the H8-BINOLate and BINOLate ligands in these
complexes were 63.2(5)° and 55.7(4)°, respectively. The larger torsional angle of the H8-
BINOLate ligand results in an increase in the bite angle of the ligand by just over 2°. Upon
dissolving dimers (meso)-6 and (meso)-7, equilibria between the homo- and heterochiral
dimers were observed. Reaction of H8-BINOL with an excess of titanium tetraisopropoxide
provided crystals of the dinuclear complex [(H8-BINOLate)Ti(O-i-Pr)2]‚Ti(O-i-Pr)4 (8).
Likewise, reaction of 2 equiv of Ti(OCy)4 (Cy ) cyclohexyl) with H8-BINOL furnished [(H8-
BINOLate)Ti(OCy)2]‚Ti(OCy)4 (9). These compounds were characterized by X-ray crystal-
lography and compared to the known [(BINOLate)Ti(O-i-Pr)2]‚Ti(O-i-Pr)4, a proposed
intermediate in the asymmetric addition of alkyl groups to aldehydes. The solution behavior
of 8 and 9 was studied by NMR spectroscopy, revealing that both complexes in solution are
in equilibrium with dimers and free titanium tetraisopropoxide. Nonlinear studies with
catalytic H8-BINOL and an excess of titanium tetraisopropoxide in the asymmetric addition
of ethyl groups to benzaldehyde showed no nonlinearity, suggesting that the equilibrium
strongly favors formation of dinuclear 8 under the conditions of the asymmetric addition.
In tr od u ction
BINOL (1,1′-bi-2-naphthol, 1, Figure 1) is one of the
most effective chiral ligands in asymmetric catalysis.1-4
It has been successfully employed with a wide range of
metal centers in a variety of Lewis acid-catalyzed
processes. Recently, hydrogenated derivatives of BINOL,
such as H8-BINOL (5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-bi-
F igu r e 1. BINOL (1), H8-BINOL (2), and H4-BINOL (3).
2-naphthol, 2)5 and H4-BINOL (5,6,7,8-tetrahydro-1,1′-
bi-2-naphthol, 3)6 have been used to facilitate asym-
metric reactions with better efficiency and enantioselec-
tivity than reactions utilizing BINOL as a chiral ligand.7
Some examples of the successful use of hydrogenated
BINOL ligands in asymmetric catalysis include nucleo-
philic epoxide opening reactions catalyzed by
(H8-BINOLate)2GaNa,8 sulfide oxidation with a tita-
nium 3,3′-dinitro-H8-BINOLate complex,9 asymmetric
olefin metathesis with molybdenum 3,3′-dialkyl-H8-
BINOLate catalysts,10,11 hetero-Diels-Alder reaction
(1) Pu, L. Chem. Rev. 1998, 98, 2405-2494.
(2) Dias, L. C. Curr. Org. Chem. 2000, 4, 305-342.
(3) Dias, L. C. J . Braz. Chem. Soc. 1997, 8, 289-332.
(4) J acobsen, E. N.; Pfaltz, A.; Yamamoto, H. Comprehensive Asym-
metric Catalysis; Springer: Berlin, 1999; Vols. 1-3.
(5) Cram, D. J .; Helgeson, R. C.; Peacock, S. C.; Kaplan, L. J .;
Domeier, L. A.; Moreau, P.; Koga, K.; Mayer, J . M.; Chao, Y.; Siegel,
M. G.; Hoffman, D. H.; Sogah, G. D. Y. J . Org. Chem. 1978, 43, 1930-
1946.
(6) Shen, X.; Guo, H.; Ding, K. Tetrahedron: Asymmetry 2000, 11,
4321-4327.
(7) Au-Yeung, T. L.-L.; Chan, S.-S.; Chan, A. S. C. Adv. Synth. Catal.
2003, 345, 537-555.
(8) Iida, T.; Yamamoto, N.; Matsunaga, S.; Woo, H.-G.; Shibasaki,
M. Angew. Chem., Int. Ed. 1998, 37, 2223-2226.
(9) Reetz, M.; Merk, C.; Naberfeld, G.; Rudolph, J .; N, G.; Goddard,
R. Tetrahedron Lett. 1997, 38, 5273-5276.
(10) Aeilts, S. L.; Cefalo, D. R.; Bonitatebus, P. J .; Houser, J . H.;
Hoveyda, A. H.; Schrock, R. R. Angew. Chem., Int. Ed. 2001, 40, 1452-
1456.
(11) Schrock, R. R.; J amieson, J . Y.; Dolman, S. J .; Miller, S. A.;
Bonitatebus, P. J .; Hoveyda, A. H. Organometallics 2002, 21, 409-
417.
10.1021/om034107h CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/03/2003

128 Organometallics, Vol. 23, No. 1, 2004
Waltz et al.
Sch em e 1. Com p a r ison of BINOL a n d
H8-BINOL-Ba sed Tita n iu m Ca ta lysts in th e
Asym m etr ic Ad d ition of Alk ylzin c a n d
Alk yla lu m in u m Rea gen ts to Ald eh yd es
F igu r e 2. Structurally characterized (H8-BINOLate)Ti
complexes.
other is a tetranuclear titanium isopropoxide di-µ3-oxo
complex (5), also with two bridging H8-BINOLate
ligands (Figure 2). In both structures, each oxygen atom
of the H8-BINOLate ligand bonds to only one
titanium center, so that the ligand spans two
titanium atoms instead of chelating to one metal. The
dihedral angles of the ligand were found to be 93° in
the dimer and 80° and 88° in the tetranuclear complex.
On the basis of these structures, it was suggested that
the large dihedral angle of the H8-BINOLate ligand is
incompatible with a chelation binding mode to tita-
nium.17
Sch em e 2. Com p a r ison of BINOL, H4-BINOL, a n d
H8-BINOL-Ba sed Tita n iu m Ca ta lysts in th e
Asym m etr ic Heter o-Diels-Ald er Rea ction
More recently, Schrock, Hoveyda, and co-workers
reported the structural characterization of 3,3′-dialkyl-
H8-BINOLate molybdenum complexes, which are cata-
lysts for the asymmetric ring-closing metathesis reac-
tion.10,11 All three of these structures are monomeric
molybdenum imido alkylidene complexes with chelating
H8-BINOLate ligands. The dihedral angle for the 3,3′-
di-tert-butyl H8-BINOLate ligand bound to molybdenum
was found to be 88.6°, which is comparable to the
dihedral angles of the bridging H8-BINOLate ligand in
Heppert’s titanium structures.
using titanium-H8-BINOLate catalysts,12,13 and alkyl
addition to aldehydes via (H8-BINOLate)Ti complexes.14,15
The (H8-BINOLate)Ti-based catalysts used in the asym-
metric addition of alkylzinc and alkylaluminum re-
agents by Chan and co-workers14,15 and the asymmetric
hetero-Diels-Alder reaction of J iang and co-workers13
are most relevant to the present study and are il-
lustrated in Schemes 1 and 2. A comparison of the
enantioselectivities with BINOL-, H4-BINOL-, and H8-
BINOL-based catalysts is presented. These reactions
employ precatalysts derived from titanium tetraisopro-
poxide and BINOL derivatives.
While the improved performance of the H8-BINOLate
ligands is often attributed to the increased steric
requirement of the ligand as a result of the larger
dihedral angle between the aromatic rings, only a
handful of transition metal H8-BINOLate complexes
have been crystallographically characterized. Heppert
and co-workers reported the first two X-ray structures
of H8-BINOL bound to a metal.16,17 One complex is a
titanium chloride dimer (4) that forms a 14-membered
ring with two bridging H8-BINOLate ligands, while the
Because of the successful application of titanium
BINOL-based catalysts to several reactions in asym-
metric catalysis and the lack of structural information
of such species, we have studied the solution and solid
state structures of this class of compounds.18,19 In the
present study we compare the structures of titanium
BINOL and H8-BINOL derivatives. Herein, we report
crystal structures of H8-BINOLate-Ti complexes in
which both oxygens of the H8-BINOLate ligand are
bound to a single titanium center. The gross structural
features of these compounds are similar to previously
reported titanium BINOLate structures;18,19 however,
the dihedral angles between the aryl rings are larger
in the H8-BINOLate complexes. Compounds derived
from H8-BINOL exhibit complex equilibria involving
dimeric and dinuclear species. The nonlinear behavior
of these compounds was examined in the asymmetric
addition of ethyl groups to benzaldehyde.
(12) Long, J .; Hu, J .; Shen, X.; J i, B.; Ding, K. J . Am. Chem. Soc.
2002, 124, 10-11.
(13) Wang, B.; Feng, X.; Huang, Y.; Liu, H.; Cui, X.; J iang, Y. J .
Org. Chem. 2002, 67, 2175-2182.
(14) Chan, A. S. C.; Zhang, F.-Y.; Yip, C.-W. J . Am. Chem. Soc. 1997,
119, 4080-4081.
(15) Zhang, F.-Y.; Chan, A. S. C. Tetrahedron: Asymmetry 1997, 8,
3651-3655.
(18) Davis, T. J .; Balsells, J .; Carroll, P.; Walsh, P. J . Org. Lett. 2001,
3, 699-702.
(19) Balsells, J .; Davis, T. J .; Carroll, P. J .; Walsh, P. J . J . Am. Chem.
Soc. 2002, 124, 10336-10348.
(16) Eilerts, N. W.; Heppert, J . A. Polyhedron 1995, 14, 3225-3271.
(17) Eilerts, N. W.; Heppert, J . A.; Kennedy, M. L.; Takusagawa,
F. Inorg. Chem. 1994, 33, 4813-4814.

Titanium(IV) Octahydrobinaphtholate Complexes
Organometallics, Vol. 23, No. 1, 2004 129
Ta ble 1. Selected Bon d Dista n ces [Å] a n d An gles [d eg] for (m eso)-6 a n d (m eso)-7
(meso)-6 (meso)-7 (meso)-6
1.858(3) 1.864(3) 3.3552(14)
(meso)-7
Ti-O(1)
Ti-O(2)
Ti′-O(2)
Ti-O(3)
Ti-O(4)
Ti-Ti′
3.382(2)
83.31(10)
110.86(10)
55.7(4)
2.138(3)
1.947(3)
1.756(3)
1.779(3)
2.140(2)
1.965(2)
1.753(3)
1.764(3)
O(1)-Ti-O(2)
85.43(11)
110.37(11)
63.2(5)
Ti-O(2)-Ti′
C(1)-C(10)-C(11)-C(20)
Resu lts a n d Discu ssion
diagram of (meso)-7 is shown in Figure 4.
Syn th esis a n d Str u ctu r e of H8-BINOLa te- a n d
BINOLa t e-Tit a n iu m Com p lexes. Heterochiral
dimer (meso)-6 was prepared by combining 1 equiv
each of Ti(O-i-Pr)4 and (rac)-H8-BINOL5 in dichlo-
romethane, resulting in
a bright yellow solution
(eq 1). Removal of the solvent and liberated 2-propanol
under reduced pressure gave a pale yellow solid
that was crystallized by dissolution in dichloro-
methane, layering with pentane, and cooling to -35 °C.
Thus, X-ray quality crystals were obtained, and the
structure of heterochiral dimer (meso)-6 is shown in eq
1. An ORTEP diagram is illustrated in Figure 3. Two
The gross structural features of heterochiral dimers
(meso)-6 and (meso)-7 are similar, consisting of [(R)-bis-
aryloxide]Ti(O-i-Pr)2 and [(S)-bis-aryloxide]Ti(O-i-Pr)2
dimerized through one oxygen of each of the bridging
aryloxide moieties. Selected bond lengths and angles are
given in Table 1. The Ti-alkoxide bond lengths of
1.756(3) and 1.779(3) Å in (meso)-6 and 1.753(3) and
1.764(3) Å in (meso)-7 are similar to those of related
compounds.18-20 The terminal O(1) and bridging O(2)
aryloxide oxygens have significantly different bond
lengths to titanium, with Ti-O(1) and Ti-O(2) bond
lengths of 1.858(3) and 2.138(3) Å in (meso)-6 and
1.864(3) and 2.140(2) Å in (meso)-7. The Ti′-O(2) bond
lengths of 1.947(3) Å in (meso)-6 and 1.965(2) Å in
(meso)-7 are shorter than the bond between the bridging
oxygen O(2) and Ti, the first titanium center. The
dihedral angle of the H8-binaphthyl rings in the
H8-BINOLate ligand is 63.2(5)° in (meso)-6, while the
BINOL derivative (meso)-7 has a smaller dihedral angle
of 55.7(4)°. Correspondingly, the O(1)-Ti-O(2) angle of
85.43(11)° in (meso)-6 is somewhat larger than that of
83.31(10)° in (meso)-7.
F igu r e 3. Thermal ellipsoid plot of (meso)-6. Ellipsoids
are at the 30% probability level. Bond distances and angles
are given in Table 1.
Use of (S)-H8-BINOL to prepare the homochiral dimer
(S,S)-6 did not result in crystalline material, and we
were not able to purify this compound by crystallization.
Nonetheless, the NMR spectral data of this complex are
informative and discussed below. In contrast to the
structure of (meso)-7, use of resolved BINOL ligand
under the conditions of eq 1 and crystallization results
in formation of the trimer [(BINOLate)Ti(O-i-Pr)2]3.18,19,21
Our previous studies in the asymmetric addition of
alkyl groups to aldehydes with (BINOLate)Ti catalysts
indicated that the dinuclear complex (BINOLate)Ti(O-
i-Pr)2‚Ti(O-i-Pr)4 was an important intermediate.19 We
set out to synthesize and characterize analogous com-
pounds prepared from H8-BINOL. Complex 8 was
prepared by reaction of 6 equiv of Ti(O-i-Pr)4 with 1
equiv of (rac)-H8-BINOL in dichloromethane (eq 2). The
resulting yellow oil was crystallized from pentane at
F igu r e 4. Thermal ellipsoid plot of (meso)-7. Ellipsoids
are at the 30% probability level. Bond distances and angles
are given in Table 1.
dichloromethane solvent molecules crystallized in the
unit cell. For the purpose of comparison, the analo-
gous reaction was performed using (rac)-BINOL and
titanium tetraisopropoxide (eq 1). Crystals were
grown at -35 °C from a mixture of dichloromethane
and 2-propanol layered with hexanes, and an ORTEP
(20) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo
and Aryloxo Derivatives of Metals; Academic Press: London, 2001.
(21) Martin, C. Design and Application of Chiral Ligands for the
Improvement of Metal-Catalyzed Asymmetric Transformations. Ph.D.
Thesis, MIT, 1989.

130 Organometallics, Vol. 23, No. 1, 2004
Waltz et al.
F igu r e 5. Thermal ellipsoid plot of 8. Ellipsoids are at
the 30% probability level. Bond distances and angles are
given in Table 2.
F igu r e 6. Thermal ellipsoid plot of 9. Ellipsoids are at
the 30% probability level. Bond distances and angles are
given in Table 2.
Ta ble 2. Selected Bon d Dista n ces [Å] a n d An gles
[d eg] for 8, 9, a n d (BINOLa te)Ti2(O-i-P r )6
groups are disordered as detailed in the Supporting
Information. The disorder is not shown in Figure 6.
Dinuclear complexes 8 and 9 can be envisioned as an
(H8-BINOLate)Ti(OR)2 fragment bound to a molecule
of Ti(OR)4 through one bridging H8-BINOLate oxygen
and one bridging alkoxide oxygen. The structural fea-
tures of 8 and 9 are similar to those of the parent
BINOL analogue (BINOLate)Ti(O-i-Pr)2‚Ti(O-i-Pr)4,18,19
as illustrated by comparison of selected bond lengths
and angles in Table 2. The Ti-alkoxide bond lengths
in 8 and 9 range from 1.763(3) to 1.802(3) Å and from
1.754(4) to 1.800(4) Å, respectively. The related
(BINOLate)Ti(O-i-Pr)2‚Ti(O-i-Pr)4 and (H8-BINOLate)-
Ti(O-i-Pr)2‚Ti(O-i-Pr)4 show similar Ti2O2 core struc-
tures. In 8 and 9, the bridging alkoxide oxygen O(5) has
a shorter bond with Ti(1), which is bound to the
H8-BINOLate ligand, than with Ti(2). Similarly, the
H8-BINOLate oxygens O(2) and O(1) have notably
different bond lengths to Ti(1) of 1.862(3) and 2.117(2)
Å in 8 and 1.885(4) and 2.139(3) Å in 9. The bridging
H8-BINOLate oxygen O(1) has a shorter bond with Ti(2)
than with Ti(1). These bond lengths are similar to those
for the analogous BINOL complex.18,19 The dihedral
angle of the H8-BINOLate rings is 61.7(4)° in 8 and
61.6(6)° in 9, whereas the BINOL complex has a smaller
dihedral angle of 54.1(5)°. The larger dihedral angle
in the H8-BINOLate derivative also results in an
increase in the O-Ti-O bond angle. In the dinuclear
H8-BINOLate derivatives 8 and 9, the O(1)-Ti-O(2)
bond angle is 84.29(10)° and 84.26(13)°, respectively,
while the same angle in the BINOLate analogue is
82.78(11)°. Thus, the H8-BINOLate ligand has a slightly
larger bite angle than the BINOLate ligand. The
dihedral angles in 8 and 9 are slightly smaller than the
dihedral angle observed in the structure of the hetero-
chiral dimer (meso)-6.
(BINOLate)-
Ti2(O-i-Pr)6
8
9
Ti(1)-O(1)
2.117(2)
1.862(3)
1.802(3)
1.773(3)
1.931(2)
1.988(2)
2.110(2)
1.790(3)
1.763(3)
1.784(3)
2.139(3)
1.885(4)
1.775(4)
1.754(4)
1.923(3)
1.976(3)
2.122(3)
1.800(4)
1.769(4)
1.785(4)
2.111(3)
1.861(3)
1.781(3)
1.779(3)
1.921(3)
1.980(3)
2.120(3)
1.794(3)
1.765(3)
1.805(3)
Ti(1)-O(2)
Ti(1)-O(3)
Ti(1)-O(4)
Ti(1)-O(5)
Ti(2)-O(1)
Ti(2)-O(5)
Ti(2)-O(6)
Ti(2)-O(7)
Ti(2)-O(8)
Ti(1)-Ti(2)
O(1)-Ti(1)-O(2)
Ti(1)-O(1)-Ti(2)
Ti(1)-O(5)-Ti(2)
3.3156(8) 3.3224(12) 3.3085(10)
84.29(10) 84.26(13) 82.78(11)
107.70(11) 107.64(14) 107.90(11)
110.18(11) 110.33(14) 109.80(12)
C(1)-C(10)-C(11)-C(20) 61.7(4)
61.6(6)
54.1(5)
-35 °C, affording X-ray quality crystals of the dinuclear
8. This complex crystallized as a pair of enantiomers in
the unit cell. The (S)-enantiomer is shown in the ORTEP
diagram in Figure 5. Selected bond lengths and angles
are given in Table 2.
Analogous to complex 8, dinuclear complex 9 was
prepared by reaction of 2 equiv of Ti(OCy)4 (Cy )
cyclohexyl) and 1 equiv of (S)-H8-BINOL in dichlo-
romethane (eq 2). X-ray quality crystals were grown
from a pentane solution at -35 °C, and the resulting
ORTEP diagram is shown in Figure 6. A molecule of
cyclohexanol cocrystallized in the unit cell but has been
omitted from the figure. Selected bond lengths and
angles are given in Table 2. Three of the cyclohexyl
The dihedral angles of 61-63° in complexes (meso)-
6, 8, and 9 are significantly smaller than those of 80-
93° in the reported H8-BINOLate complexes of tita-
nium17 and molybdenum.10,11 The larger dihedral angle
in Heppert’s H8-BINOLate-titanium complexes can be
explained by the fact that the H8-BINOLate ligand
bridges two titanium centers, so that each H8-BINOLate

Titanium(IV) Octahydrobinaphtholate Complexes
Organometallics, Vol. 23, No. 1, 2004 131
Sch em e 3. P r op osed Mech a n ism for
Rea r r a n gem en t of Heter obin u clea r Com p ou n d 8
oxygen is bound to a different titanium atom, requiring
a larger dihedral angle for this configuration. The
reported molybdenum complexes do have a chelated H8-
BINOLate ligand bound to one metal center through
both oxygens. However, the ligand is substituted at the
3,3′ position with bulky alkyl groups that serve to
increase the dihedral angle through steric interactions
and inhibit dimerization through steric shielding. In
addition, the larger size of the molybdenum center
allows for chelation of the H8-BINOLate ligand, thus
accommodating a larger dihedral angle, whereas the
smaller titanium center in (meso)-6, 8, and 9 forces the
ligand to adopt a smaller dihedral angle in order to
retain bonding in a chelating fashion.
The titanium-H8-BINOLate complexes (meso)-6, 8,
and 9 all have similar structural features. The H8-
BINOLate oxygens are bound unequally to one titanium
center, and the bridging H8-BINOLate oxygen forms a
shorter bond with the second titanium center. For
compounds 8 and 9 with bridging alkoxide groups, the
bridging alkoxide oxygen has a shorter bond with the
titanium center that is bound to both H8-BINOLate
oxygens. These trends have been observed previously
for BINOLate-titanium-isopropoxide complexes in the
literature.18,19,22 Given the enhanced performance of H8-
BINOL over BINOL in certain catalytic asymmetric
reactions, complexes (meso)-6, 8, and 9 are surprisingly
similar in structure to the analogous BINOLate deriva-
tives.18 While the dihedral angles of all three H8-
BINOLate complexes are roughly the same, they are
approximately 7° larger than those of their BINOLate
derivatives. Increasing the dihedral angle of the ligand
results in a small increase in the bite angle of the ligand.
Thus, an increase in the O-Ti-O bond angle may also
be important. This difference in the dihedral angle and
the bite angle is likely responsible for the observed
difference in catalytic performance, since the structural
features of the H8-BINOLate complexes are similar to
those of the BINOLate complexes.
Solu tion NMR Sp ectr a of 6-9. The 1H NMR
spectrum of the material formed on reaction of (S)-H8-
BINOL with 1 equiv of Ti(O-i-Pr)4 (eq 1) shows two
aromatic doublets and one isopropoxide methyne reso-
nance, all of equal integration. This simplicity is also
observed in the 13C{1H} NMR spectrum, which shows
one isopropoxide methyne resonance and six aromatic
carbon resonances. The C2-symmetry implied by these
simple NMR spectra may arise in solution by the dimer
(S,S)-6 undergoing an intramolecular exchange of H8-
BINOLate ligands via cleavage of one bond between
each titanium and bridging oxygen, as proposed by
Heppert and co-workers to explain the C2-symmetry
observed in the solution spectra of the similar homo-
chiral dimer [(3,3′-Me2-BINOLate)Ti(O-i-Pr)2]2.22
Unlike the simple solution spectra of homochiral
dimer (S,S)-6, the spectra of (meso)-6 appear more
complex. When crystals of (meso)-6 are dissolved in
CDCl3, the solution appears to contain an equilibrium
mixture of the hetero- and homochiral dimers, as
evidenced by the 1H and 13C{1H} NMR spectra. The
aromatic region of the 1H NMR spectrum of (meso)-6
shows four doublets of equal integration. The isopro-
poxide methyne hydrogens appear as three resonances
in a 2:1:1 ratio. The 13C{1H} NMR spectrum of (meso)-6
shows two downfield resonances for the aromatic ipso-
carbons and three resonances for the isopropoxy
1
OCHMe2. All of the resonances that appear in the H
and 13C{1H} NMR spectra for the homochiral dimer
(S,S)-6 match perfectly with peaks that appear in the
spectra of (meso)-6 in solution, which is evidence that
an equilibrium mixture is established in solution.
Similar to that of (meso)-6, the 1H NMR spectrum of
the BINOL derivative (meso)-7 also shows three reso-
nances for the isopropoxide methyne hydrogens in a
2:1:1 ratio. Solution molecular weight studies of (BINO-
Late)Ti(O-i-Pr)2 indicated that it is a dimer,21 although
it is a trimer in the solid state.18,21 All of the resonances
1
in the H and 13C{1H} NMR spectra of the homochiral
dimer [(BINOLate)Ti(O-i-Pr)2]2 also appear in the solu-
tion spectra of (meso)-7, which indicates that an equi-
librium mixture of homo- and heterochiral dimers exists.
Since crystals of dinuclear complex 8 were difficult
to grow without 6 equiv of Ti(O-i-Pr)4, the excess Ti(O-
i-Pr)4 swamped the alkyl and alkoxide regions of the
1H NMR spectrum, leaving a clear view of only the
aromatic region, which shows six doublets in a 1:2:1:1:
2:1 ratio. The two large doublets are most likely the
dinuclear 8, although we would expect to see four
doublets for the static structure shown in eq 2. The (H8-
BINOLate)Ti(O-i-Pr)2 moiety probably undergoes a
rapid exchange of the bound Ti(O-i-Pr)4 with free Ti-
(O-i-Pr)4 that exists in excess in the solution, resulting
in two sets of equivalent aromatic hydrogens. This could
be an associative process, going through an intermediate
of the type (H8-BINOLate)Ti(O-i-Pr)2‚2[Ti(O-i-Pr)4]. The
BINOL derivative (BINOLate)Ti(O-i-Pr)2‚2[Ti(O-i-Pr)4]
is stable in the solid state, and the structure has been
reported.18 On dissolving, this compound loses 1 equiv
of Ti(O-i-Pr)4 to give (BINOLate)Ti(O-i-Pr)2‚Ti(O-i-Pr)4
and free Ti(O-i-Pr)4. It is also possible that the dinuclear
species undergoes an intramolecular rearrangement by
breaking the Ti(2)-O(1) bond, pseudorotation about the
five-coordinate Ti(1), and recoordination of an alkoxide
by Ti(1). Both of these mechanisms depicted in Scheme
3 have been suggested by Heppert to explain the C2-
symmetry observed in the room-temperature solution
NMR spectra of the dinuclear (3,3′-Me2BINOLate)Ti-
(O-i-Pr)2‚Ti(O-i-Pr)4.22
(22) Boyle, T. J .; Barnes, D. L.; Heppert, J . A.; Morales, L.;
Takusagawa, F.; Connolly, J . C. Organometallics 1992, 11, 1112-1126.

132 Organometallics, Vol. 23, No. 1, 2004
Waltz et al.
The four smaller aromatic doublets in the solution
1
spectrum of crude 8 match those seen in the H NMR
spectrum of the heterochiral dimer (meso)-6, consisting
of (meso)-6 and (S,S)-6. Thus, 8 is in equilibrium with
small amounts of hetero- and homochiral dimers and
free Ti(O-i-Pr)4. This result is in contrast to earlier
results with the BINOL derivative (BINOLate)Ti(O-i-
Pr)2‚Ti(O-i-Pr)4, where only the dinuclear complex is
observed.18 A 1H NMR spectrum matching that of 8 was
obtained from titrating (meso)-6 with Ti(O-i-Pr)4 in 2
equiv increments. The spectrum gradually changed from
that described for (meso)-6 to the spectrum matching
that described above for 8 after about 8 equiv of Ti(O-
i-Pr)4 with respect to (meso)-6 had been added. After
addition of 4 equiv of Ti(O-i-Pr)4, roughly equal amounts
of dinuclear 8, (meso)-6, and (S,S)-6 existed in solution.
After 14 equiv of Ti(O-i-Pr)4 had been added to (meso)-
6, the product was predominately the dinuclear complex.
This result suggests that excess Ti(O-i-Pr)4 breaks up
the dimeric (meso)-6 and (S,S)-6 to establish an equi-
librium between dinuclear 8, (meso)-6, and (S,S)-6. A
similar experiment involving titration of (S,S)-6 with
excess Ti(O-i-Pr)4 also results in the conversion of the
majority of the homochiral dimer to the dinuclear
species with the same two large doublets in the 1H NMR
spectrum as was seen for 8. Reaction of resolved and
racemic H8-BINOL with 2 equiv of Ti(O-i-Pr)4 results
in mostly homochiral and a mixture of homo- and
heterochiral dimers, respectively, in solution by 1H NMR
and only a small amount of dinuclear species. These
NMR experiments show that the dimeric complexes
form preferentially over the dinuclear species, which
require an excess of added Ti(O-i-Pr)4. This result is in
contrast to the behavior of the structurally similar
dinuclear complex (BINOLate)Ti(O-i-Pr)2‚Ti(O-i-Pr)4,
which forms as the major product upon reaction of (rac)-
BINOL with 2 equiv of Ti(O-i-Pr)4.18
F igu r e 7. Plot of data from nonlinear effect experiments.
otherwise act to break up the dimer and form the
dinuclear species.
Mech a n istic Stu d ies of Dieth ylzin c Ad d ition to
Ald eh yd es Med ia ted by H8-BINOL/Ti(O-i-P r )4. H8-
BINOL recently has been shown to give better enanti-
oselectivity than BINOL in the diethylzinc addition to
aldehydes (97.6 vs 91.9% ee for benzaldehyde, Scheme
1), yet little is known about the mechanism.15 Given the
complex equilibrium observed in the NMR spectra of 6,
8, and 9, we investigated the nonlinear behavior of these
compounds in the asymmetric addition of ethyl groups
to benzaldehyde. Following the general procedure of
Zhang and Chan,15 we examined the asymmetric addi-
tion reaction with H8-BINOL of varying ee to determine
if a nonlinear effect exists under catalytic conditions.
The experiment was run with H8-BINOL of 20, 40, 60,
80, and 100% ee, in addition to 1.6 equiv of Ti(O-i-Pr)4
and 3 equiv of ZnEt2 with respect to benzaldehyde
substrate. A ligand loading of 10 mol % H8-BINOL was
used for these experiments, as this amount was found
to be the lowest that still gives the maximum ee of 98%
reported in the literature. The nonlinear effect experi-
ments were performed at -20 °C so that the reaction
would be slow enough to monitor by removing aliquots
at varying time points. The reactions reached comple-
tion at 4 h, and the ee’s were constant over time. No
nonlinear effects were observed for this catalytic system,
as can be seen by the straight-line plot of the data in
Figure 7.
The absence of nonlinear effects in the catalytic
addition of ZnEt2 to benzaldehyde makes it unlikely that
dimeric species are involved in the reaction. Instead,
the dinuclear species 8 may be formed as a result of
the excess Ti(O-i-Pr)4, which is critical to the efficiency
and enantioselectivity of the reaction. As illustrated by
the NMR titration experiment described above, the
presence of about 7 equiv of Ti(O-i-Pr)4 with respect to
H8-BINOL is necessary to convert the majority of the
dimeric species into the dinuclear complex in solution.
This observation would explain Zhang and Chen’s
finding that a 1:7 ratio of H8-BINOL to Ti(O-i-Pr)4 was
optimal in their diethylzinc additions to aldehydes.15 It
must be noted that an absence of nonlinear effect may
be observed even though dimers are formed during the
asymmetric reaction. As seen in the NMR studies
described above, the homo- and heterochiral dimers
1
The H NMR spectrum of crystals of dinuclear com-
plex 9, prepared from the resolved H8-BINOL ligand,
shows two aromatic doublets in a 1:1 ratio. The alkoxide
methyne protons appear as two resonances in a 1:2
ratio, the smaller resonance belonging to the (H8-
BINOLate)Ti(OCy)2 portion and the larger resonance
attributed to the Ti(OCy)4 moiety. The 13C{1H} NMR
spectrum shows one aromatic ipso-carbon resonance and
three alkoxide OCHMe2 resonances. The simplicity of
these spectra suggests a high degree of symmetry that
does not exist in the static dinuclear structure in eq 2.
The dinuclear species 9 most likely exists in solution
as the homochiral dimer [(H8-BINOLate)Ti(OCy)2]2 and
free Ti(OCy)4. The NMR spectra of a 1:1 mixture of Ti-
(OCy)4 and (S)-H8-BINOL, which presumably form the
homochiral dimer [(H8-BINOLate)Ti(OCy)2]2, exhibit the
1
same H and 13C{1H} NMR resonances as the solution
spectra of 9. Rearrangement processes such as those
described for (S,S)-6 may account for the observed C2-
symmetry of 9 in solution, which appears to exist as the
homochiral dimer and free Ti(OCy)4. No dinuclear
species is observed by NMR when crystals of 9 are
dissolved in CDCl3. Unlike 8, which was prepared with
6 equiv of Ti(O-i-Pr)4 and whose NMR was obtained in
the presence of the unreacted Ti(O-i-Pr)4, crystalline 9
in solution contains no extra Ti(OCy)4, which would

Titanium(IV) Octahydrobinaphtholate Complexes
Organometallics, Vol. 23, No. 1, 2004 133
exist in solution in roughly equal amounts (Keq ≈ 1).
This equilibrium would result in no observable nonlin-
ear behavior in the asymmetric reaction if monomers
are the reactive species or if the diastereomeric dimers
have the same reactivity. This scenario is unlikely,
however, due to the large excess of Ti(O-i-Pr)4 in the
reaction which would react with monomer and dimers
to form the dinuclear species (H8-BINOLate)Ti(O-i-Pr)2‚
Ti(O-i-Pr)4. Interestingly, the same lack of nonlinear
effects was observed for the asymmetric addition reac-
tion to aldehydes under similar conditions, using BINOL
as the chiral ligand and 120 mol % Ti(O-i-Pr)4.19
enantioselectivity of these ligands in asymmetric ca-
talysis.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out in dry
glassware under nitrogen using standard glovebox or Schlenk
line techniques. All solvents were dried and distilled prior to
use. Titanium tetraisopropoxide and benzaldehyde were dis-
tilled prior to use. NMR spectra were recorded on a Bruker
360 MHz or AM500 MHz NMR spectrometer. Chemical shifts
are reported relative to residual protiated solvent or tetram-
ethylsilane. Enantiomeric excesses were determined on a
Hewlett-Packard 6890 gas chromatograph with a 30 m Supelco
â-DEX. H8-BINOL was prepared according to the literature
procedure.5 Tetrakis(cyclohexyloxy)titanium was prepared
from cyclohexanol and titanium tetraisopropoxide.
Con clu sion s
Three new structures of titanium-H8-BINOLate-iso-
propoxide were studied crystallographically in the solid
state and in solution by NMR spectroscopy. These
structures were compared to their BINOLate analogues
that were previously published and (meso)-7, which is
reported here. Excess Ti(O-i-Pr)4 breaks up the dimeric
species to form the dinuclear species in solution. These
dimeric and dinuclear titanium complexes show that
even though the H8-BINOLate ligand has a larger
dihedral angle and steric requirement than the more
common BINOLate ligand, the H8-BINOLate ligand can
bind in a chelating fashion to one titanium center to
form complexes that are very similar in structure to
those obtained from the BINOLate ligand. In addition,
the fact that both H8-BINOL- and BINOL-based cata-
lysts show no nonlinear effects for the catalytic asym-
metric addition reaction to aldehydes suggests that
these two catalysts may react in a mechanistically
similar fashion, possibly forming a dinuclear species
containing two titanium atoms but only one bisphenox-
ide ligand. Given the similarity in solid state structure
of known (BINOLate)Ti complexes and the (H8-BINO-
Late)Ti derivatives described here, the difference in
dihedral angle (about 7°) may account for the enhanced
performance of H8-BINOL over BINOL as a chiral
ligand for some catalytic asymmetric reactions. The
differences in catalytic activity of H8-BINOLate versus
BINOLate complexes may also be the result of differing
solution behavior of these compounds. While the BINO-
Late and H8-BINOLate complexes appear to have
similar solid state structures, the solution behavior
illustrates some differences. In solution, the dinuclear
BINOLate complex forms easily with stoichiometric
amounts of starting materials and does not require
excess titanium alkoxide. On the other hand, the
addition of excess titanium alkoxide is necessary to form
the dinuclear H8-BINOLate complex, which establishes
an equilibrium in solution with both homo- and hetero-
chiral dimeric species and free titanium alkoxide. In the
absence of excess titanium alkoxide, the dimeric H8-
BINOLate species appears to be more stable and form
in preference to the dinuclear form containing two
titanium atoms but only one H8-BINOLate ligand. The
opposite is true of the BINOLate compounds, where the
dinuclear form appears to be more stable than the
dimeric form in solution. These differences in solution
behavior, coupled with the difference in dihedral angles
for H8-BINOLate and BINOLate titanium alkoxide
complexes, may provide some insight into the differing
[(R)-H8-BINOLa te][(S)-H8-BINOLa te]Ti2(O-i-P r )4 [(m e-
so)-6]. To a stirred suspension of racemic H8-BINOL (125.0
mg, 0.425 mmol) in 5 mL of dichloromethane was added 1
equiv of Ti(O-i-Pr)4 (120.7 mg, 0.425 mmol) in 5 mL of
dichloromethane. The resulting bright yellow solution was
stirred for 30 min, and the volatiles were removed under
vacuum. The pale yellow residue was redissolved in dichlo-
romethane, and the volatiles were again removed under
vacuum. This process was repeated a third time to ensure
complete removal of the liberated 2-propanol. X-ray quality
crystals were grown by dissolving the pale yellow solid in
dichloromethane and layering with pentane at -35 °C. 1H
NMR (500 MHz, CDCl3): δ 6.83 (d, J ) 8.2 Hz, 2H), 6.71 (d,
J ) 8.2 Hz, 2H), 6.65 (d, J ) 8.1 Hz, 2H), 6.47 (d, J ) 7.8 Hz,
2H), 4.50 (quin, J ) 6.0 Hz, 2H), 4.35 (quin, J ) 6.1 Hz, 1H),
4.10 (quin, J ) 6.0 Hz, 1H), 2.72 (m, 6H), 2.63 (m, 2H), 2.49
(m, 2H), 2.41 (m, 2H), 2.13 (m, 4H), 1.73 (m, 2H), 1.68 (m,
10H), 1.51 (m, 4H), 1.15 (2H), 1.07 (m, 10H), 1.03 (d, J ) 5.3
Hz, 6H), 0.68 (d, J ) 5.2 Hz, 6H). 13C{1H} NMR (360 MHz,
CDCl3): δ 158.94, 157.79, 136.44, 136.36, 130.83, 130.64,
128.24, 128.10, 126.08, 125.56, 117.58, 117.10, 80.95, 80.48,
79.65, 29.62, 29.59, 27.97, 25.97, 25.78, 25.69, 25.23, 23.46,
23.38, 23.31.
[(S)-H8-BINOLa te]2Ti2(O-i-P r )4 [(S,S)-6]. To a stirred
suspension of (S)-H8-BINOL (125.5 mg, 0.426 mmol) in 5 mL
of dichloromethane was added 1 equiv of Ti(O-i-Pr)4 (121.2 mg,
0.426 mmol) in 5 mL of dichloromethane. The resulting amber
solution was stirred for 30 min, and the volatiles were removed
under vacuum. The orange-yellow solid was redissolved in
dichloromethane, and the volatiles were again removed under
vacuum. This process was repeated a third time to ensure
complete removal of the liberated 2-propanol. The resulting
compound is presumably the homochiral dimer, but we were
not able to obtain crystalline material for a structural deter-
1
mination. H NMR (360 MHz, CDCl3): δ 6.71 (d, J ) 8.1 Hz,
4H), 6.47 (d, J ) 7.4 Hz, 4H), 4.49 (m, 4H), 2.70 (m, 8H), 2.40
(m, 4H), 2.12 (m, 4H), 1.69 (m, 12H), 1.50 (m, 4H), 1.06 (m,
24H). 13C{1H} NMR (360 MHz, CDCl3): δ 157.75, 136.28,
130.54, 128.04, 125.50, 117.03, 80.38, 29.55, 27.89, 25.89,
25.62, 23.39, 23.31.
[(R)-BINOLa te][(S)-BINOLa te]Ti2(O-i-P r )4 [(m eso)-7].
To a stirred suspension of racemic BINOL (9.5 mg, 0.0332
mmol) in 0.2 mL of dichloromethane was added 1 equiv of Ti-
(O-i-Pr)4 (9.8 µL, 0.0332 mmol) and 25 equiv of 2-propanol (64
µL, 0.836 mmol). After stirring for 15 min, the orange solution
was layered with hexanes and cooled to -35 °C, affording
X-ray quality crystals. This compound can also be prepared
without 2-propanol and crystallized from a dichoromethane
solution layered with hexanes. 1H NMR (500 MHz, CDCl3): δ
7.86 (m, 8H), 7.49 (d, J ) 8.6 Hz, 2H), 7.36 (m, 5H), 7.30 (m,
5H), 7.17 (m, 8H), 6.77 (br m, 2H), 4.52 (quin, J ) 5.8 Hz,
2H), 4.40 (br s, 1H), 3.65 (br s, 1H), 1.11 (d, J ) 6.0 Hz, 9H),
1.05 (d, J ) 6.1 Hz, 9H), 1.03 (m, 6H), 0.28 (d, J ) 4.1 Hz,
6H). Strongest resonances in 13C{1H} NMR (500 MHz,

134 Organometallics, Vol. 23, No. 1, 2004
Waltz et al.
Ta ble 3. Am ou n ts of Liga n d for Non lin ea r Effect
Exp er im en t
CDCl3): δ 159.15, 133.31, 130.30, 129.05, 128.25, 128.17,
127.14, 125.61, 123.55, 121.39, 81.21, 77.44, 25.89, 25.63.
(H8-BINOLa te)Ti2(O-i-P r )6 (8). To a stirred suspension of
racemic H8-BINOL (10.0 mg, 0.0340 mmol) in 5 mL of
dichloromethane was added 6 equiv of Ti(O-i-Pr)4 (57.9 mg,
0.204 mmol) in 5 mL of dichloromethane. The resulting yellow
solution was stirred for 30 min, and the volatiles were removed
under vacuum. The pale yellow residue was redissolved in
dichloromethane, and the volatiles were again removed under
vacuum. This process was repeated a third time to ensure
complete removal of the liberated 2-propanol. X-ray quality
crystals were grown from pentane at -35 °C. The unit cell
% ee H8-BINOL
(S)-H8-BINOL
(rac)-H8-BINOL
20
40
60
80
5.0 mg
10.0 mg
15.0 mg
20.0 mg
20.0 mg
15.0 mg
10.0 mg
5.0 mg
increments, with the 1H NMR spectra being recorded after
each addition. A total of 45.5 µL (0.152 mmol) of Ti(O-i-Pr)4
was added to each tube.
Rea ction of (R)- a n d (r a c)-H8-BINOL w ith 2 Equ iv Ti-
(O-i-P r )4. To each stirred suspension of (R)-H8-BINOL (40.0
mg, 0.136 mmol) and (rac)-H8-BINOL (40.0 mg, 0.136 mmol)
in 5 mL of dichloromethane was added 2 equiv of Ti(O-i-Pr)4
(77.2 mg, 0.272 mmol) in 5 mL of dichloromethane. The
resulting solutions were stirred for 30 min, and the volatiles
were removed under vacuum. The residues were redissolved
in dichloromethane, and the volatiles were again removed
under vacuum. This process was repeated a third time to
1
contains cocrystallized enantiomers. H NMR of crude mate-
rial, aromatic region (360 MHz, CDCl3): δ 6.83 (d, J ) 8.2
Hz, 1H), 6.78 (d, J ) 8.2 Hz, 2H), 6.71 (d, J ) 8.2 Hz, 1H),
6.66 (d, overlapping, 1H), 6.62 (d, J ) 8.2 Hz, 2H), 6.47 (d, J
) 7.8 Hz, 1H).
[(S)-H8-BINOLa te]Ti2(OCy)6 (9). To a stirred suspension
of (S)-H8-BINOL (100.0 mg, 0.340 mmol) in 5 mL of dichlo-
romethane was added 2 equiv of Ti(OCy)4 (302.0 mg, 0.679
mmol) in 5 mL of dichloromethane. The resulting yellow
solution was stirred for 30 min, and the volatiles were removed
under vacuum. X-ray quality crystals were grown from pen-
tane at -35 °C. A molecule of cyclohexanol cocrystallized with
1
ensure complete removal of the liberated 2-propanol. The H
and 13C{1H} NMR spectra were recorded in CDCl3.
Non lin ea r Effect Exp er im en t. (S)-H8-BINOL and (rac)-
H8-BINOL were weighed in the amounts shown above in Table
3 into four 10 mL Schlenk flasks equipped with stirbars to
give 20, 40, 60, and 80% ee of (S)-H8-BINOL (0.0849 mmol
total). Dichloromethane (6.8 mL) was added to each flask,
followed by titanium tetraisopropoxide (407 µL, 1.36 mmol),
and the resulting orange solutions were stirred for several
minutes. A 1.0 M solution of diethylzinc (2.55 mL, 2.55 mmol)
in hexanes was added to each flask via syringe. The solutions
were then cooled to -20 °C, benzaldehyde (87 µL, 0.853 mmol)
was added, and the solutions were stirred for 4 h. Samples of
each of the four reactions were quenched with 1 M HCl,
extracted with pentane, dried over magnesium sulfate, filtered
through Celite, and analyzed by chiral GC.
1
the titanium complex. H NMR (360 MHz, CDCl3): δ 6.71 (d,
J ) 8.1 Hz, 2H), 6.48 (d, J ) 7.5 Hz, 2H), 4.20 (br s, 2H), 4.05
(br s, 4H), 3.54 (br s, 1H, CyOH), 2.70 (m, 4H), 2.38 (m, 2H),
2.10 (m, 2H), 1.83 (br s, 14H) 1.66 (m, 22H), 1.48 (m, 8H), 1.20
(m, 35H). 13C{1H} NMR (360 MHz, CDCl3): δ 157.79, 136.31,
130.58, 128.02, 125.54, 117.16, 86.34, 82.66, 70.56, 64.87,
36.91, 35.79, 35.57, 29.62, 27.91, 25.90, 25.82, 25.68, 24.41,
23.91, 23.85, 23.48, 23.41.
[(S)-H8-BINOLa te]2Ti2(OCy)4. To a stirred suspension of
(S)-H8-BINOL (125.0 mg, 0.425 mmol) in 5 mL of dichlo-
romethane was added 1 equiv of Ti(OCy)4 (188.7 mg, 0.425
mmol) in 5 mL of dichloromethane. The solution was stirred
for 30 min, and the volatiles were removed under vacuum. The
resulting oil is presumably the homochiral dimer plus free
cyclohexanol, but we were not able to obtain crystalline
Ack n ow led gm en t. This work was supported by the
National Institutes of Health (National Institute of
General Medical Sciences, GM58101).
1
material for a structural determination. H NMR (360 MHz,
CDCl3): δ 6.71 (d, J ) 8.1 Hz, 4H), 6.48 (d, J ) 7.6 Hz, 4H),
4.20 (br s, 4H), 3.53 (br s, 4H, free CyOH), 2.70 (m, 8H), 2.44
(m, 4H), 2.10 (m, 4H), 1.65 (m, 54H), 1.14 (m, 42H). 13C{1H}
NMR (360 MHz, CDCl3): δ 157.73, 136.26, 130.52, 128.00,
125.48, 117.08, 86.30, 80.37, 70.54 (br), 64.7 (br), 35.73, 35.55,
29.56, 27.87, 25.73, 25.58, 24.6 (br), 23.88 (br), 23.42, 23.35.
NMR Titr a tion Exp er im en ts. Crystals of heterochiral
dimer (meso)-6 (10.0 mg, 0.0109 mmol) and noncrystalline
homochiral dimer (S,S)-6 (10.0 mg, 0.0109 mmol) were each
dissolved in 0.4 mL of CDCl3 and transferred to separate NMR
tubes. After the 1H NMR spectra were recorded, Ti(O-i-Pr)4
(6.5 µL, 0.0217 mmol) was added to each tube, which was
inverted several times to ensure dissolution. The 1H NMR
spectra were recorded, and Ti(O-i-Pr)4 was added in 6.5 µL
Su p p or tin g In for m a tion Ava ila ble: Detailed informa-
tion on the crystal structure determinations, including tables
of data collection parameters, final atomic positional and
thermal parameters, and interatomic distances and angles as
well as ORTEP diagrams of (meso)-6, (meso)-7, 8, and 9. NMR
spectra of (meso)-6, (S,S)-6, (meso)-7, 8, 9, titration experi-
ments, reaction of (R)- and (rac)-H8-BINOL with 2 equiv Ti-
(O-i-Pr)4, and reaction of (S)-H8-BINOL with 1 equiv Ti(OCy)4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM034107H